Some prior automobile theft prevention devices include a theft prevention switch connected to the starter circuit for an engine. When an automobile door is locked by means of a key or the like from a position outside the automobile, the theft prevention switch is automatically opened so as to make it impossible to subsequently start the engine even if the engine starting switch is turned to the ON position, unless the door is subsequently legally or properly unlocked by means of the key or the like.
Within such an automobile theft prevention device or system, the locking of the door is detected by means of a door lock/unlock detector associated with a door lock device or a linkage mechanism coupled to the door lock device.
It has been tedious and time-consuming to install the door lock/unlock detector in its proper operative position since the door lock device or the linkage mechanism has its components arranged in a complex manner and at a position at which the door lock/unlock detector is to be located, and in addition, since a member to be detected by means of the door lock/unlock detector is displaced in accordance with a complex movement pattern.